I. Field of the Invention
The present invention relates generally to the field of heavy duty demolition shears that are mountable on equipment such as backhoes or power shovels and have manipulatable booms that are powered hydraulically. More particularly, it provides resistance to spreading of cutter blades and a replaceable cutter point that is positional on an end of a pivotal cutter jaw with cutter blades. The replaceable cutter point and cutter blades on the cutter jaws are adjustable in closeness to a stationary cutter jaw with cutter blades by means of selectively positioning a pivot bearing and linear thrust abutments of the pivotal cutter jaw linearly on a cutter axle in pivotal relationship between the pivotal cutter jaw and the stationary cutter jaw. The replaceable cutter point and cutter blades are maintainable in select closeness to the stationary cutter jaw by means of slidable contact of an extension of the pivotal cutter jaw against a surface of the stationary cutter jaw or by optional slidable contact of the replaceable cutter point against a replaceable bearing surface on the stationary cutter jaw.
II. Description of the Prior Art
Heavy duty metal demolition shears mounted on backhoes have proven very effective in the last several decades They are used variously for demolishing, cutting and handling large discarded metal objects and structures having metal girders, pipe, beams, cable and other items for recycling or disposal A wide variety of such demolition shears have been developed and used previously. None, however, are known to have a sufficiently steady and sturdy means for adjusting and maintaining precise closeness of cutting relationship between stationary and pivotal cutter jaws and between a replaceable cutter point on a pivotal jaw and stationary cutter edges in cutting relationship to the replaceable cutter point
For cutting metal with any type of metal cutting means, the same as with powered demolition shears, steadiness and precision of cutter positioning are critical When optimum positioning and straight cutting of a metal cutter are lost due to looseness of fit, or when a shear blade vacillates due to unsteadiness, flexibility or bending, cutting action veers off at an angle. The metal being cut then abrades, distorts, overheats and in various ways destroys the metal cutter in addition to losing cutting efficiency. In heavy duty demolition shears, the most obvious symptom or effect is spreading of distance between the jaw blades. Like a flexible pair of scissors, the blades spread apart, become dull and loose effectiveness. This condition is far more pronounced and detrimental in metal cutting than in cutting more pliable material, however, due to the incompressible nature and abrasiveness of metal.
This metal cutting principle has not been recognized sufficiently for its effective application in demolition shears previously. Results have been short use life and less cutting efficiency than can be achieved with this invention
Examples of different but pertinent prior art are described in the following patent documents.
______________________________________ COUNTRY NUMBER DATE NAME ______________________________________ U.S. 4,897,921 Feb. 6, 1990 Ramun U.S. 4,872,264 Oct. 10, 1989 LaBounty U.S. 4,686,767 Aug. 18, 1987 Ramun et al U.S. 4,670,983 Jun. 9, 1987 Ramun et al U.S. 4,558,515 Dec. 17, 1985 LaBounty U.S. 4,519,135 May 28, 1985 LaBounty ______________________________________
The Ramun 1990 patent described replaceable blades on shear jaws, including a replaceable shear point, and means for guiding shearing motion of shear blades. But it did not teach a means for adjustment of a jaw guiding means and adjustment of a linear thrust bearing means in coordination with a guide means as taught by this invention. The LaBounty 1989 patent taught a plate shearing device with neither a replaceable shear point nor an adjustable blade positioning means in combination with an adjustable linear thrust bearing. The Ramun et al August 1987 patent taught a replaceable cutter tip and an adjustable thrust bearing. But its thrust bearing was adjustable in only one direction. There was no coordinated adjustment of travel guide for cutter jaws and the means for adjustment of the thrust bearing was different than taught by this invention. The Ramun et al June, 1987 patent was not significantly different from the Ramun et al August, 1987 patent in relation to the same features. The LaBounty December, 1985 patent did not teach either a replaceable cutter tip nor a jaw travel guide separately from a pivotal axle. The LaBounty May, 1985 patent described a form of pressure plate that arrested side travel of the pivotal cutter jaw. But it was not adjustable either separately or in conjunction with linear positioning of the pivotal cutter blade on a pivot axle as taught by this invention. No single patent known in the prior art and no combination of known prior art is believed to provide the advantages and features of this invention without inventive change.